The present invention relates to a light modulator device used for a display for the presentation of two- and/or three-dimensional image contents or image sequences. The light modulator device comprises a light modulator and a control unit. The phase and/or the amplitude of a substantially collimated light wave field are alterable by the light modulator in dependence on the location on the light modulator. The light modulator is controllable by the control unit. The present invention further relates to a display and to a manufacturing method for a light modulator device.
Holographic displays comprising a spatial light modulator (SLM) with a matrix arrangement of pixels are known in prior art. For example, there are light modulators which can change or modulate the phase or the amplitude or both the phase and the amplitude (i.e. complex-valued) of the light which interacts with the SLM.
Only to give an example, reference is made to an autostereoscopic display (ASD) according to WO 2005/060270 A1, where the current eye positions of at least one observer are detected and where the stereoscopic images are deflected towards the left and the right eye of the observer, respectively, dependent on the current eye positions. This is realised by means of a backplane shutter device. As far as holographic displays are concerned, reference is made to WO 2006/066919 A1 or WO 2006/027228 A1 to give some examples. Higher diffraction orders are generated in a Fourier plane of such a holographic display. The distance between these diffraction orders is reciprocally proportional to the pixel pitch of the SLM of the display, i.e. the centre-centre distance between the periodic structures of the light modulator. For holographic displays with an observer window, a diffraction order must comprise at least the size of this observer window. The pixel pitch of the SLM is therefore to be chosen to match the desired size of the observer window. Since the observer window only has to be somewhat larger than the diameter of an eye pupil, a relatively large pixel pitch is resulting, with typical values ranging between 30 μm and 50 μm.
Moreover, however, a holographic reconstruction will only become visible if one eye of the observer is positioned in the observer window. Therefore, the observer has to remain in a fixed position, or the observer window has to be tracked to the current position of the observer eyes. For this, it is necessary to provide an eye detection device and a beam tracking device. Prior art beam tracking devices, such as the light source tracking device described in WO 2006/119920 A1 or the electrowetting cell tracking device described in WO 2008/142108 A1, are complex and costly.
It is further known in the prior art to realise the function of a field lens, which can either be provided as a separate unit or be integrated into the tracking device. This field lens function serves to focus light from different positions of the display to a desired position in an observer plane. For example, Z tracking, i.e. tracking of the observer window in the axial direction of the display (i.e. when the observer eyes move towards the display or away from the display), requires an alterable field lens function.
However, it is also possible to achieve beam tracking by software means, i.e. by way of alterable encoding, as described for example in WO 2006/066906 A1. According to that method, linear phase profiles are encoded in the pixels of the SLM, as the case may be in addition to a hologram. However, the angular range in which tracking by encoding can be reasonably used is also restricted by the pitch of the SLM. Generally, the tracking range can comprise several diffraction orders when using that method, the intensity of the tracked observer window being reduced according to the reduced intensity of the respective higher diffraction orders. A reasonable tracking range would thus typically include one or at most two to three diffraction orders.
Generally, it is also possible to use an SLM with a smaller pixel pitch. A reasonable motion range of an observer in front of a holographic display requires an angle of a few degrees. Though this would demand a pitch in a range of few micrometres. For example, a 24-inch display with a pitch of 2 μm would result in about 40 billion pixels, which would not be feasible as regards the manufacturing, the addressing and the computerised generation of real-time holographic information.